The present invention relates to a gyro used for detecting the rotation angular velocity, more particularly, to a tuning fork type vibration gyro having two arms and a base formed in one-piece.
Gyroscopes have been used as means for identifying the position of moving objects such as airplane, large vessels, space satellites, and the like. Recently, they have been utilized for detecting vibration of apparatus such as a car navigation system and video camera. Among such gyroscopes, research and development of a tuning fork type vibration gyro having a constitution comprising two arms and a base for supporting the two arms, which are formed in one-piece by a piezoelectric monocrystal, have been pursued.
FIG. 1 is, for example, a structural view of a tuning fork type vibration gyro disclosed in Japanese Patent Application Laid-Open (Tokukaihei) No. 9-269228(1997). In FIG. 1, numeral 1 denotes a tuning fork type vibrator. The tuning form type vibrator 1 has two arms 2, 3 and a base 4 for supporting the arms 2 and 3. The arms 2, 3 and base 4 are formed in one-piece by processing a piezoelectric monocrystal such as LiTaO3, LiNbO3, etc. By coupling the base 4 of this tuning fork type vibrator 1 to a supporting substrate 6 mounted on a stem 5, the tuning fork type vibrator 1 is supported.
Moreover, a horizontal section of a supporting arm 7 having a substantially U-shaped cross section is inserted into a slit of the supporting substrate 6 formed to include the center of rotational motion of the supporting substrate 6, and attached flexibly to the supporting substrate 6 through an adhesive layer 8 formed of a rubber-like elastic body. Both of the end sections of the supporting arm 7 are provided with a protrusion, and these protrusions are inserted into holes formed in the stem 5.
Furthermore, in order to cover and protect these members, a cap 9 is provided. The cap 9 and the stem 5 form a case 10. Besides, a circuit substrate 11 (see FIG. 5) including a later-described drive circuit for exciting drive vibration and a detection circuit for processing a detection signal may be provided on the stem 5 and/or the cap 9 so as to be housed in the case 10.
As shown in FIGS. 2(a) and 2(b), such a tuning fork type vibrator 1 includes fx mode vibration (in-plane vibration) and fy mode vibration (plane-vertical vibration). When drive vibration (in-plane vibration) is exited, if a rotational angular velocity is applied, detection vibration (plane-vertical vibration) occurs, and then an output signal proportional to the magnitude of this vibration is detected so as to find the angular velocity.
By the way, denoting a drive vibration (in-plane vibration) direction, a detection vibration (plane-vertical) vibration direction and a rotation axis direction perpendicular to both of these directions as the X direction, Y direction and Z direction, respectively, when external vibration or impact is applied to the X direction and Y direction particularly, the tuning fork type vibrator 1 produces oscillating motion as shown in FIGS. 3(a) and 3(b) together with the supporting substrate 6.
In this case, as shown in FIGS. 4(a) and 4(b), the tip of the tuning fork type vibrator 1 (arms 2 and 3) bumps first against the inner wall of the case 10, that is, the stem 5 or the cap 9. Besides, if the circuit substrate 11 is mounted on the inner wall of the case 10, as shown in FIGS. 5(a) and 5(b), the tip of the tuning fork type vibrator 1 (arms 2 and 3) bumps first against the circuit substrate 11. Here, if external vibration or impact is great, the tuning fork type vibrator 1 is destroyed as it is broken at the joint section of the arms 2 and 3 by this impact, causing a problem that the tuning fork type vibrator 1 can not perform the function of a sensor.
Various ideas for protecting the tuning fork type vibrator from external vibration or impact have been proposed (Japanese Patent Application Laid-Open (Tokukaihei) No. 5-18755(1993) (prior art 1) and No. 7-243857(1995) (prior art 2)).
In the prior art 1, a cushioning member and a protecting member are illustrated. This cushioning member is provided between a cover to which a supporting member for supporting the tuning fork type vibrator is secured and a case surrounding the cover, and has the function of absorbing external vibration. Moreover, the protecting member provided in the vicinity of the outside of both of the ends of the supporting member of the tuning fork type vibrator has the function of preventing an excessive displacement of the tuning fork type vibrator, i.e., a large plastic deformation of the supporting member.
However, in this prior art 1, if vibration with a very high accelerating rate is applied, the cushioning member can not absorb this vibration. Consequently, the supporting member has a plastic deformation, and the center axis of the tuning fork type vibrator is displaced from the initial set position, resulting in significant deterioration of gyro characteristics. In addition, there is a possibility that the plastic deformation of the supporting member is further increased by impact, etc. and the tuning fork type vibrator remains contact with the surrounding members. In such a case, since the drive vibration is stopped, the tuning fork type vibrator can not perform the function of a gyro sensor at all.
Meanwhile, the prior art 2 discloses a structure which solves the problem associated with the prior art 1 and is effective to resist external impact. A cushioning member for absorbing external impact is provided between a work plate and a plate to which a supporting member for supporting a tuning fork type vibrator is attached; between a circuit substrate to which the work plate is attached and a case; and between the work cover attached to the work plate and a case. In the structure of this prior art 2, a cushioning member is provided between respective adjacent members among the outermost case, the circuit substrate housed in the case, a shield cover of the circuit substrate, the work cover, the work plate and the tuning fork type vibrator so as to successively absorb external impact by the respective cushioning members.
However, in this prior art 2, since a large number of the cushioning members are provided, there is a problem that the overall structure is not made compact. Moreover, in the event where the tuning fork type vibrator remains contact with the surrounding members, it can not perform the function of a gyro sensor at all like the prior art 1.
Incidentally, in a tuning fork type vibration gyro having a basic structure as shown in FIG. 1, when the center axis of rotation of the tuning fork type vibrator 1 and the supporting axis of the supporting arm 7 are perfectly aligned with each other, for example, even if external vibration in the Y direction is applied, the tuning fork type vibrator 1 produces only translation vibration as shown in FIG. 6 because the upper and lower moments with respect to the line of the supporting axis as the boundary are equal. However, it is difficult to align these axes with each other, and if external vibration in the Y direction is applied when these axes are not aligned with each other, the upper and lower moments with respect to the line of the supporting axis as the boundary are unbalanced, and a rotational motion is produced as shown in FIG. 7. Thus, there is a problem that, even when a rotational motion is not applied to the tuning fork type vibrator 1, an unnecessary rotational motion signal is detected.
The principal object of the present invention is to provide a tuning fork type vibration gyro capable of preventing destruction of a tuning fork type vibrator due to external vibration or impact with a compact structure.
Another object of the present invention is to provide a tuning fork type vibration gyro capable of decreasing an unnecessary signal, which is produced when external vibration is applied.
A tuning fork type vibration gyro of a first aspect, which is a tuning fork type vibration gyro comprising a tuning fork type vibrator including two arms and a base and a supporting substrate for supporting the base, is characterized by comprising an oscillation limiting member disposed at a position in a direction to the base from a joint section of the arms, for limiting an amplitude of oscillation of the tuning fork type vibrator.
In the tuning fork type vibration gyro of the first aspect, the oscillation limiting member for limiting the amplitude of oscillation of the tuning fork type vibrator caused by external vibration or impact is provided at an arbitrary position to the base from the joint section of the arms of the tuning fork type vibrator (the boundary section between the arms and base) where in-plane vibration does not occur. Hence, this oscillation limiting member prevents the tuning fork type vibrator from bumping against the surrounding members, and thereby preventing destruction of the tuning fork type vibrator.
A tuning fork type vibration gyro of a second aspect, which accords with the first invention, is characterized by further comprising an adhesive layer between the tuning fork type vibrator and the supporting substrate for bonding the tuning fork type vibrator and supporting substrate together and characterized in that the oscillation limiting member is secured to either the tuning fork type vibrator, the supporting substrate or the adhesive layer.
In the tuning fork type vibration gyro of the second aspect, the oscillation limiting member is provided on at least one of the tuning fork type vibrator, supporting substrate and adhesive layer, and it is possible to readily dispose the oscillation limiting member.
A tuning fork type vibration gyro of a third aspect, which accords with the first invention, is characterized by further comprising a case for housing the tuning fork type vibrator and supporting substrate, and characterized in that the oscillation limiting member is disposed between the tuning fork type vibrator and the case.
A tuning fork type vibration gyro of a fourth aspect, which accords with the first aspect, is characterized by further comprising a circuit substrate connected with the tuning fork type vibrator, and characterized in that the oscillation limiting member is secured to the circuit substrate.
In the tuning fork type vibration gyro of the third or fourth aspect, the oscillation limiting member is disposed between the tuning fork type vibrator and the case or between the tuning fork type vibrator and the circuit substrate, and this oscillation limiting member prevents the tuning fork type vibrator from bumping against the circuit substrate or the case.
A tuning fork type vibration gyro of a fifth or sixth aspect, which accords with the third or fourth invention, is characterized in that a clearance between the arm and the case or a clearance between the arm and the circuit substrate is not smaller than a predetermined value.
In the tuning fork type vibration gyro of the fifth or sixth aspect, since the position and shape of the oscillation limiting member are arranged so that the clearance between the tuning fork type vibrator and the case or the clearance between the tuning fork type vibrator and the circuit substrate is not smaller than the predetermined value, the tuning fork type vibrator can never bump against the case or the circuit substrate.
A tuning fork type vibration gyro of a seventh or eighth aspect, which accords with the fifth or sixth aspect, is characterized by simultaneously satisfying equations
H=Lxc3x97sin xcex8 greater than 0, and
tan xcex8=(Hxe2x88x92Hxe2x80x2)/Lxe2x80x2
where H is a distance between the tuning fork type vibrator and the case or the circuit substrate, L is a distance between a center of oscillation of the tuning fork type vibrator and supporting substrate and a tip of the tuning fork type vibrator, Hxe2x80x2 is a distance between the case or the circuit substrate and a position at which the tuning fork type vibrator or the supporting substrate comes into contact with the oscillation limiting member when the tuning fork type vibrator oscillates, and Lxe2x80x2 is a distance between a center of oscillation of the tuning fork type vibrator and supporting substrate and a position at which the tuning fork type vibrator or the supporting substrate comes into contract with the oscillation limiting member when the tuning fork type vibrator oscillates.
In the tuning fork type vibration gyro of the seventh or eighth aspect, the position and shape of the oscillation limiting member are arranged so as to satisfy the above equations, and thus the tuning fork type vibrator does not bump against the case or the circuit substrate.
A tuning fork type vibration gyro of a ninth aspect, which accords with the first aspect, is characterized in that the oscillation limiting member is formed from a material selected from the group consisting of elastic bodies of epoxy resins, urethane resins, silicone rubbers and butyl rubbers, and foam materials thereof
In the tuning fork type vibration gyro of the ninth aspect, a material as those mentioned above is used for the oscillation limiting member, and thus it is possible to readily mass-produce the oscillation limiting member even if it has a complicated shape.
A tuning fork type vibration gyro of a tenth aspect, which accords with the ninth aspect, is characterized in that a hardness of the oscillation limiting member is not more than 100 (JIS A).
In the tuning fork type vibration gyro of the tenth aspect, the hardness of the oscillation limiting member is arranged not to exceed the above-mentioned numerical value, thereby preventing the tuning fork type vibrator from being broken.
A tuning fork type vibration gyro of an eleventh aspect, which is a tuning fork type vibration gyro comprising a tuning fork type vibrator including two arms and a base, and a supporting substrate for supporting the base, for performing in-plane vibration of the tuning fork type vibrator as drive vibration and twisted vibration of the tuning fork type vibrator and supporting substrate as one body as detection vibration, is characterized in that an absolute value of a difference between a resonant frequency of the drive vibration and a resonant frequency of the detection vibration is not smaller than an upper limit of a required frequency characteristic.
In the tuning fork type vibration gyro of the eleventh aspect, the absolute value of the difference between the resonant frequency of drive vibration and the resonant frequency of detection vibration is arranged not to be smaller than the upper limit of the required frequency characteristic, thereby decreasing an unnecessary signal due to external vibration.
A tuning fork type vibration gyro of a twelfth aspect, which accords with the eleven aspect, is characterized in that the absolute value of the difference is at least three times the upper limit of the required frequency characteristic.
In the tuning fork type vibration gyro of the twelfth aspect, the absolute value of the difference is arranged to be at least three times the upper limit of the required frequency characteristic, thereby producing a great effect of decreasing an unnecessary signal due to external vibration.
A tuning fork type vibration gyro of a thirteenth aspect, which is a tuning fork type vibration gyro comprising: a tuning fork type vibrator including two arms and a base; a circuit for exiting drive vibration: a detection circuit for detecting detection vibration that occurs when a rotational angular velocity is applied; and a signal processing circuit for converting a detection signal of the detection circuit into a digital signal and processing the digital signal, wherein a sampling frequency of the signal processing circuit is greater than two times a reciprocal number of an integral time in the signal processing, is characterized in that an absolute value of a difference between a resonant frequency of the drive vibration and a resonant frequency of the detection vibration is greater than the reciprocal number of the integral time.
In the tuning fork type vibration gyro of the thirteenth aspect, the sampling frequency of the digital signal processing circuit of a detection system is arranged to be greater than two times the reciprocal number of the integral time in the signal processing, and the absolute value of the difference between the resonant frequency of drive vibration and the resonant frequency of detection vibration is arranged to be greater than the reciprocal number of the integral time, thereby decreasing an unnecessary signal due to external vibration.